A machine for dispensing stackable roofing washers individually from a stack of such washers and for driving fasteners through such washers is exemplified in Beach et al. U.S. Pat. Nos. 4,890,968, 5,042,142, and 5,056,684. Such a machine is useful for fastening one or more layers of roofing material, such as a roofing membrane or one or more layers of roofing insulation, to an underlayment.
As exemplified in the patents noted above, the washer-dispensing features of the machine comprise a base, a shuttle mounted movably to the base, and a mechanism for moving the shuttle. The shuttle is movable to a washer-releasing position relative to the base and to a washer-engaging position relative thereto and is biased to the washer-releasing position. The shuttle is adapted to remove a lowermost washer from the stack and to cause movement of the lowermost washer to a discharge position by positive engagement of the shuttle with the lowermost washer when moved from the washer-engaging position to the washer-releasing position. The shuttle-moving mechanism, which is actuatable by a user, moves the shuttle from the washer-releasing position to the washer-engaging position when actuated. Such mechanism, which is deactuated normally, permits the shuttle to return to the washer-releasing position when deactuated. Such washer-dispensing and fastener-driving machines are available commercially from ITW Buildex (a division of Illinois Tool Works Inc.) of Itasca, Ill., under its ACCUTRAC trademark.
Stackable roofing washers useful in such washer-dispensing and fastener-driving machines are available commercially from ITW Buildex, supra, in plural sizes having different features and including relatively large, generally square, stamped steel washers and relatively small, generally circular, stamped steel washers with plastic inserts. As used commonly over a layer of roofing insulation, such relatively large, generally square, stamped steel washers are exemplified in Beach et al. U.S. Pat. Nos. 4,890,968 and 5,042,142. As used commonly over roofing membranes, such relatively small, generally circular, stamped steel washers with plastic inserts are exemplified in Beach et al. U.S. Pat. No. 5,056,684.
It would be highly desirable to have a single machine that could be selectively adapted to dispense washers of either size. However, efforts to develop such a selectively adaptable machine having a shuttle that could be alternatively used with washers of either size have been unsuccessful heretofore, primarily because it has been found that such relatively small washers have an undesirable tendency to move with the shuttle when the shuttle is moved from the washer-releasing position. Such tendency is due to friction.